The US and South Korea have commenced the joint and combined ground, air, naval and special operations field exercise, Foal Eagle 2017.
More than 3,600 US service members have been deployed to join the 28,000 US troops already based in South Korea to participate in the annual exercise.
The two-month long exercise has been designed to enhance South Korea's combat readiness and defences, as well as maintain stability on the Korean Peninsula.
It forms a part of the US-South Korean Mutual Defense Treaty signed in October 1953, the US Department of Defense (DoD) said in a statement.
US DoD spokesman Navy captain Jeff Davis said: “These exercises are defensive in nature, and they have been carried out regularly, openly and transparently for nearly 40 years.”
Scheduled to conclude on 30 April, Foal Eagle 2017 is also expected to demonstrate the US's commitment to its alliance with South Korea.
Recently South Korea's fifth-largest conglomerate Lotte International approved a land swap deal with the government, allowing it to install the US terminal high altitude area defense (THAAD) system.
The US and South Korea are considering the viability of a THAAD system operated by US Forces Korea to counter North Korean missile threats.
Davis added: “It remains our intent to have [THAAD] there and in an operational state as soon as feasible.
“This is a critical measure that we're taking to defend the Korean people and alliance forces against North Korean missile threats, a very serious threat as highlighted by the 12 February ballistic missile launch by North Korea.”